Control of the motion of a reciprocating member

ABSTRACT

In a method of operating a yarn traversing mechanism of the kind in which a reciprocating member is driven from a power source through at least one force-transferring member and in which the motion of the reciprocating member is adapted to be damped by a damping device, the improvement which comprises: detecting the time of zero velocity of the reciprocating member; actuating the damping device at a point in time between said zero velocity and a point when the increment of velocity of the reciprocating member above the desired velocity is a maximum if no damping is applied; and deactuating the damping device after such a short time that the damping does not cause undesirable distortion of the force-transferring member.

United States Patent 1151 3,656,291 Key 61' al. 1451 Apr. 18, 1972 [s41 CONTROL OF THE MOTION OF A 3,575,385 11/1951 Killoran ..242/26.l

RECIPROCATING MEMBER 3,245,215 4/1966 Graf ..'.....57/99 [72] Inventors: Kenneth Andrew Key, Abergavenny; Clive Williams Hoop r, wp r b of Primary Examiner-Stanley N. Gilreath gland Assistant Examiner--Werner H. Schroeder [73] Assignee: Imperial Chemical Industries Limited, Attorney-filmmam Darby8 Cushman London, England 22 Filed: Dec. 16, 1970 [57] ABSTRACT [21] APPL 98,718 In a method of operating a yarn traversing mechanism of the kind in which a reciprocating member is driven from a power Related U.S. Application Data source through at least one force-transferring member and in which the motion of the reciprocating member is adapted to [63] gg f 'z g of 780519 be damped by a damping device, the improvement which a an one comprises: detecting the time of zero velocity of the reciprocating member; actuating the damping device at a [30] Fol-mg Apphcamn Pnomy Data point in time between said zero velocity and a point when the Dec. 8, 1967 Great Britain ..55,964/67 increment of velocity of the reciprocating member above the desired velocity is a maximum if no damping is applied; and [52] U.S. Cl... ..57/l56, 57/99, 242/261 deactuating the damping device after such a short time that [51] Int. Cl. ..D01h 13/06 the damping does not cause undesirable distortion of the [58] Field of Search ..57/156, 95, 99; 242/261, 26.2, force-transferring member.

[56] References Cited 4 Claims, 4 Drawing Figures UNITED STATES PATENTS 1,245,453 11/1917 Gastonguay ..242/26.4

[IA/4,97 a meuze Z2 Z4 awn/=22 pmpaeame fQflA/JflUdF/Z g l f) 3g [5 CONTROL OF THE MOTION OF A RECIPROCATING MEMBER This is a continuation-in-part of application Ser. No. 780,5 l9, filed Dec. 2, 1968, now abandoned.

The present invention relates to the control of the motion of a reciprocating member and relates particularly, though not exclusively, to the control of the motion of a yarn traversing guide, for example, the ring-rail of a drawtwisting machine.

It is well known to wind yarn to form a package by traversing the yarn backwards and forward along the axis of a rotating container, usually a cylinder. The pattern of the traversing motion throughout the building of the package can in practice be quite complicated, with the object of obtaining a package shape which is stable and which does not give rise to such difficulties as snatching when the yarn is later removed from the package.

In many traverse motions employed in practice complicated accelerations and decelerations of the traversing member take place. Such accelerations and decelerations are particularly critical near the end of the traverse stroke where the traversing member approaches its reversal point, then decelerates to zero velocity and then reverses its direction of travel.

The present invention is described with reference to simple motion, but of course the principles involved are entailed in the reversal of the motion of any reciprocating member.

In the drawings:

FIG. 1 is a diagrammatic time-motion plot of the position of a member reciprocating up and down with uniform velocity, near and at its upper reversal point, (A), against time. This figure is intended to illustrate one form of an ideal desired motion;

FIG. 2 is a similar plot, but illustrating undesirable oscillations at (B) after the reversal point (A);

FIG. 3 is a plot illustrating undesirable rounding" of the reversal point by the use of certain prior damping devices; and

FIG. 4 is a diagrammatic illustration of one form of damping system embodying the principles of the present invention.

In practice, a reciprocating member is driven from some power source, such as an electric motor, through one or more force-transferring members. Such members are normally of metal or other resilient material.

At the reversal point, (A) in FIG. I, relatively large amounts of energy must be applied to stop the moving member and reverse its direction of motion. Part of this applied energy is stored up in the said resilient force-transferring members, as in a spring, and is then released again once the reciprocating member has started traveling in the opposite direction (downwards in FIG. 1). The practical result of this effect is that the reciprocating member is catapulted in such opposite direction by the above said stored-up excess energy and thus moves faster than it should do away from the reversal point. An oscillating movement of the reciprocating member is thus set up, which is gradually damped out, as illustrated in FIG. 2 at (B). Such oscillatory motion of the ring rail of a drawtwist machine is usually called bounce and, using suitable techniques, time-motion plots similar to that shown diagrammatically in FIG. 2 can be obtained directly from the machine.

It will readily be appreciated that such bounce will manifest itself in the form of ridges or other undesirable forms in the shape of the package build. On removing the yarn from such a package the yarn in troughs" may snatch against the hills," producing undesirable tension variations in the yarn and even leading to breaks.

Clearly, one way to overcome such bounce is to apply a damper to the reciprocating member, for instance a damper operating on the principle of viscous drag or friction, in order to damp out such oscillations, and this is a common means employed in the trade to obviate the before-mentioned difficulties. If the damper is fitted on a drawtwisting machine in such a way that it is in operation all the time, however, as is the usual practice in the trade, it will also tend to damp the motion of the reciprocating member excessively at the reversal point (A) and a plot similar to that shown in FIG. 3 may be obtained.

The round top of FIG. 3 indicates that the reversal is slow and that the ring-rail actually dwells at the reversal point (A). This dwell leads to a rather thicker layer of yarn being laid on the package at this point, and this effect will give rise to undesirable ridge formation.

A further, very great, disadvantage of constant damping is evinced when the machine is run at high speeds, entailing high accelerations of the reciprocating member. At such speeds the stresses imposed by damping are such that the force-transferring members of the machine become distorted, perhaps permanently.

High speed operation is becoming more and more widely used and speeds are tending to increase and the application of damping even for very short periods may distort or even break the force-transferring members.

Thus, the problem arises of how to approach an ideally sharp reversal point as illustrated at (A) in FIG. 1, without the subsequent bounce, as illustrated at (B) in FIG. 2, and with the minimum application of damping.

We have found that a way of overcoming the above problem is to have no added damping on the ring-rail during most of the time of its travel but to apply the damper just at the right moment, at or after the reversal point, in such a way as to absorb the above said stored-up energy which gives rise to the bounce, and then, when this excess energy is absorbed, and when the member is approaching and near to the desired constant velocity, to take the damper off again. For the reasons given above the damping should be removed as the member is approaching and is near to the desired constant velocity. In this way two objects are achieved:

a. the application of damping can be so short (i.e., a few milliseconds) that the force-transferring members have no time to feel and respond to it and hence do not become distorted.

b. if the damping is kept on, the force-transferring members will again store up energy which, when the damping is removed, will again catapult the reciprocating member forward at an undesirably high velocity and so induce bouncing again. Short application avoids this.

The present invention accordingly comprises the application of damping to a reciprocating member in a controlled fashion, and for such a short time that said damping does not cause undesirable distortion of the driving, force-transferring,

member or members moving said reciprocating member, in order to produce a desired motion of the said reciprocating member.

An example of the present invention, by way of clarification and in no way limiting of the invention, is illustrated in FIG. 4. A conventional drawtwisting machine was equipped with a reciprocating ring-rail 10 including a spinning ring 9 for guiding a yarn 8 onto a package 7. The machine was also equipped with a conventional hydraulic clamping device 11 and a control system activation of the damping device 11 at a point in the path of travel of the ring-rail 10 at or just after its reversal, said point being determined by experiment, and which deactivated the damping device 11 at another suitable point. Such an in-out mechanism can be installed to operate at one or both ends of the traverse stroke of the ring-rail 10, as required.

The ring-rail 10 is reciprocated up and down by any suitable means, such as a force-transmitting member in the form of a pivoted lever 12 which is oscillated about its axis by a motor M. The clamping device 11 includes a piston 13 connected to the ring-rail 10 for movement therewith by a piston rod 14.

In the present example the control circuit includes a linear velocity transducer 16 (for example, Type D2866/I manufac tured by Penny & Giles, Christchurch, Bournemouth, Hants, England) connected to the ring-rail 10 for detecting zero speed of the ring-rail 10, i.e., the exact reversal point. The signal from the transducer 16 is a small voltage which is proportional to the velocity of the ring-rail 10. This signal is amplified in a preamplifier 18 (such as Type ZA2 manufactured by Fenlow Electronics Ltd., Webridge, Surrey, England) and is fed to a high speed strip chart recorder 20. The signal also feeds a comparator 22 (such as Type uA710C manufactured by 8.0.8. Fairchild, London, England) which changes the polarity of its output as the input crosses zero, i.e., as the ringrail 10 reaches zero velocity. The signal from the comparator 22 is shaped by a pulse shaper 24 (such as Type P510 manufactured by Mullard Equipment Ltd, Crawley, Sussex, England) to give it a sharp leading edge suitable for triggering a first monostable multivibrator 26 (such as TUIO manufactured by Mullard Equipment Ltd). This device produces a single pulse, the duration of which may be coarsely set by a fixed capacitor and finely set by a variable resistor 28. The duration of this pulse is the time between the ring-rail l attaining zero velocity and the moment of application of the damping. The trailing edge of the pulse from the monostable vibrator 26 triggers a second monostable vibrator 30 of similar construction. This produces a single pulse which may be finely adjusted by a variable resistor 32 and which is the duration of application of damping. This pulse is amplified using a power amplifier 34 (such as Type RDlO manufactured by Mullard Equipment Ltd.) and is employed to operate a two-way solenoid valve 36 connected into the hydraulic circuit of the damping device 11. Operation of the valve 36 causes hydraulic fluid to flow through a restriction 38 rather than through the main passage 39, thus increasing damping. A hydraulic pump P fitted with a suitable hydraulic pressure relief valve (not shown) causes the hydraulic system to be under pressure and prevents air bubbles and cavitation effects as the piston 13 moves up and down with the ring-rail 10.

It will be seen from the above description that the monostable vibrators 26 and 28 function as two timing circuits one of which actuates the damping device 11 and the other of which deactuates the damping device. The exact points at which the damping should be applied and removed will vary with the speed, weight, etc., of the reciprocating ring-rail 10 and of the force-transmitting member 12, and in practice the points are determined experimentally for any given machine, using the chart recorder 20 to observe the velocity profile of the ringrail 10. In general, a damping period of a few milliseconds (for example, milliseconds) up to about 100 milliseconds is appropriate. In the illustrated embodiment the duration of damping was 40 milliseconds at which time the ring-rail had been brought back to nearly the desired constant speed. Of course, there is some uncertainty in the time of operation of the various components and fine adjustment is necessary for the best results.

In the present example, the amount of damping applied was also brought to the minimum necessary to produce the desired result, by adjustment of the variable restriction 38 on the damper. Damping, with the reciprocating ring-rail 10 moving at an average speed of l3 inches per min. and the damper piston 13 moving at 26 inches per min. was found to be effective in the range of about 20,000 to 50,000 poundals, per foot, per second.

Operation of the present invention as described in this example greatly reduced ring-rail bounce and it would be expected that further careful experimentation would reduce it to negligible proportions.

It is clear from the above description that means for operating the present invention can be applied to any reciprocating member, although for clarity it has been described with particular reference to a drawtwister ring-rail.

The operating means described is of a simple type and many other more sophisticated arrangements could be developed by those skilled in the art, employing for instance more complex electronic devices. The operation of the damping means could depend on other factors than the velocity of the reciprocating member, such, for instance, as its position or acceleration.

In this way, although only dampers using viscous drag or friction have been mentioned, it is clear that any other form of damping, or energy-absorbing means could be employed within the scope of this invention,

Although the description herein refers to putting-1n or taking-out of damping completely, for some purposes, of course, it may be necessary only to increase or decrease damping and this could clearly be done using the teaching of the present invention.

Finally, although the description particularly relates to the reversal points of a reciprocating member, the invention could be applied to any other point in the motion of a reciprocating member where necessary.

What is claimed is:

1. In a method of operating a mechanism of the kind in which a reciprocating member is driven from a power source through at least one force-transferring member at a desired velocity and in which the motion of the reciprocating member is adapted to be damped by a clamping device, the improvement which comprises: detecting the time of zero velocity of the reciprocating member; actuating the damping device for a period of time between said zero velocity and a point when the velocity of the reciprocating member reaches said desired velocity, and deactuating the clamping device after such a short period of time that the damping does not cause undesirable distortion of the force-transferring member.

2. A method as in claim 1 wherein the duration of damping is in the range of about 5-100 milliseconds.

3. A method as in claim 1 wherein the reciprocating member is a traversing guide for use in the building of a yarn package.

4. A method as in claim 1 wherein the reciprocating member is a drawtwister ring-rail. 

1. In a method of operating a mechanism of the kind in which a reciprocating member is driven from a power source through at least one force-transferring member at a desired velocity and in which the motion of the reciprocating member is adapted to be damped by a damping device, the improvement which comprises: detecting the time of zero velocity of the reciprocating member; actuating the damping device for a period of time between said zero velocity and a point when the velocity of the reciprocating member reaches said desired velocity, and deactuating the damping device after such a short period of time that the damping does not cause undesirable distortion of the force-transferring member.
 2. A method as in claim 1 wherein the duration of damping is in the range of about 5- 100 milliseconds.
 3. A method as in claim 1 wherein the reciprocating member is a traversing guide for use in the building of a yarn package.
 4. A method as in claim 1 wherein the reciprocating member is a drawtwister ring-rail. 